1. Field of the Invention
The invention relates generally to matrix-addressed displays and, more particularly, to addressing circuits for control thereof.
2. Description of the Related Art
Displays are typically composed of a two-dimensional matrix of pixels, each of which may comprise a light-emitting device, such as a laser, a light-emitting diode (LED), or an organic light-emitting device (OLED), or a light-modulating device. Such displays generally include an addressing circuit for activating the matrix of pixels in either an active or a passive manner. In a typical passive addressing circuit, each pixel is located at the intersection of row and column data lines that determine which pixels in the matrix will be activated. A selected pixel is activated by passing current through the particular row and column lines that have been activated. Passive addressing techniques, however, require very high instantaneous currents to drive each light-emitting device because each pixel is activated only momentarily as the entire matrix is scanned and further because most light emission processes have a short lifetime relative to the scanning rates for the addressing lines.
Active matrix circuits, in contrast, have used transistors to control the current driving the light-emitting devices. In prior two-transistor designs, a gating transistor is controlled by two input data lines to set the state of a driving transistor, which controls the current supplied to the light-emitting device. The two input data lines for all of the pixels may be collectively arranged as two groups corresponding with the rows and columns of a two-dimensional matrix. One group of the input lines controls the light emission intensity of the pixel, while the other group provides the timing waveforms that control the application of the light emission intensity information to the pixel.
The state of the driving transistor is maintained by a storage capacitor coupled to the gate of the driving transistor. Unfortunately, a rather sizeable storage capacitor is required to compensate for the deleterious effect of the leakage current of the gating transistor. Further, the driving transistor has a substantial voltage drop (at least several volts) when in an "ON" state for supplying current to the light-emitting device. Still further, transistors may also be undesirable for their incompatibility with certain substrates, such as glass, which are favored for use with particular light-emitting devices (e.g., OLEDs).